Friday, July 1, 2016

The Edwards and
Trinity Aquifers provide critical water resources to Central Texas. Streams
that create the beautiful Texas Hill Country are in fact hydrologically linked
to the aquifer (groundwater) systems. Aquifers provide springflows that sustain
the streams, and the streams, in turn, recharge the aquifers.

Many studies, going back
decades, document the surface and groundwater interactions in the Edwards
Aquifer. However, despite the growing demand for water and increasing threats
to surface water resource from both ecological and human health perspectives,
few studies have been conducted to understand those interactions in the Hill
Country Trinity Aquifers of Central Texas. The purpose of this document is to
summarize new information from recent studies along the Blanco River (Smith et
al., 2015) and Onion Creek (Hunt et al., in press). These studies provide a
greater understanding of the surface water and groundwater resources in the
area that could help guide policies for groundwater and surface-water
management, and also guide future scientific studies.

Both studies used
similar methods that included measuring losses and gains of stream flow to
identify recharge and springflow areas. Other methods used included measuring
water levels from wells and water chemistry. Results from these studies have
common conclusions for both the Blanco River and Onion Creek, including:

Complex surface and groundwater
interactions with alternating gaining
and losing reaches present during both high and low creek-flow conditions.
Gaining reaches are due to the presence of springs and spring-fed tributaries
that increase flows in the streams, while losing reaches result from
recharge features (sinkholes, fractures, and caves) that drain water from
the stream into the aquifer;

Losing portions of the streams
provide recharge to the Upper and Middle Trinity Aquifers; and,

Gaining portions of the streams
over the Trinity Aquifers provide for recharge downstream to the losing
reaches over the Edwards Aquifer,
which provide base flow to Barton and San Marcos Springs.

In summary, these
studies provide strong evidence that water flowing in the Blanco River and
Onion Creek are recharging the Trinity and Edwards Aquifers along certain
reaches of the streams. The greatest uncertainty of these studies is how much,
how quickly, and under what conditions does recharge occur into the Trinity
Aquifer.

To address these
uncertainties scientists are continuing to collect hydrogeologic data and
planning additional studies. Future studies could involve dye tracing to
determine the fate of the surface water after it enters the aquifer, additional
flow measurements, more extensive water-level measurements, and further
geochemical analyses of groundwater and surface water.

Drought Rules

Either Barton Springs OR the Lovelady Well can trigger a drought declaration by the Board. However, BOTH Barton Springs AND the Lovelady Well must be above their respective drought trigger levels to exit a drought declaration.